Electronic devices, such as wireless communication devices, have become increasingly popular due, in part, to their portability. Portability is accomplished by equipping the device with a battery. The battery, prior to depletion, supplies power to operate components of the device. Once the voltage of the battery depletes to a low battery threshold below which the components can only operate for a short time, the device initiates a controlled power down.
Most electronic devices have circuitry configured such that without a controlled power down operation, the device continues to operate until the voltage level of the battery reaches a power-on reset (POR) threshold at which the device immediately, and without warning, turns off. Such power down that is immediate and without warning can be problematic if critical operational processes are left incomplete, such as the establishment of communication with a remote device or the internal execution of a function that must be brought to completion once started, such as data storage operations. Also, in such situations, the user of the device will be given no warning that the device will be turned off.
One component of the device that is powered by the battery is a power amplifier. In operation, the power amplifier amplifies signals to an output level sufficient for over the air transmission. During operation, the power amplifier may enter a saturation state in which it cannot amplify signals to the output level demanded of it by the control circuitry of the device. While saturated, the power amplifier draws excessive current from the battery in an attempt to meet the demands of the control circuitry. In circumstances where the power amplifier is saturated while the battery voltage is low, the excessive current drain of the power amplifier can cause the battery to fully deplete before the controlled power down can be executed or cause the controlled power down to be executed prematurely.
One existing way to minimize rapid battery depletion is described in U.S. Pat. No. 5,278,994 by Black et al., entitled "Power Amplifier Saturation Detection and Correction Method and Apparatus," issued on Jan. 11, 1994, and assigned to Motorola, Inc. In U.S. Pat. No. 5,278,994, the output level of the power amplifier is decreased whenever saturation is detected. In one embodiment, saturation is detected by sensing a slow-down of the control loop response. Once detected, the output level is reduced by an amount based on the level of saturation, which is determined from the loop response time. Because loop response time is not perfectly correlated with the level of saturation, there is a need to slightly over-correct the power level in order to reliably predict depletion of the battery. Such over-correction compromises power amplifier performance.
Although U.S. Pat. No. 5,278,994 provides one way to minimize rapid battery depletion, it would be beneficial to be able to maximize amplifier performance and to ensure that the controlled power down is always executed.